This application is based on Japanese Patent Application No. 2001-266637 filed on Sep. 4, 2001 the contents of which are incorporated herein by reference.
1. Field of the Invention
The present invention relates to a fuel vapor control system that prevents fuel vapor from being emitted to the atmosphere, specifically the fuel vapor control system having a controller for performing a self leak check.
2. Description of Related Art
The fuel vapor control system has a canister that contains an adsorbent for adsorbing fuel vapor from a fuel tank during operation of a fuel consuming device such as when an engine is not activated. The fuel vapor adsorbed in the canister is desorbed and purged into the engine when the engine is activated and the fuel vapor is consumed. In the fuel vapor control system, a purge valve is disposed between the canister and an intake pipe of the engine in order to control a purge amount in an appropriate amount. Further, in order to control a communication between the canister and the atmosphere, a canister valve is disposed between the canister and the atmosphere.
In order to ensure the function of the fuel vapor control system, it is important to detect a leak on the fuel vapor control system in an early stage. The leak may be detected by monitoring an internal pressure of the fuel vapor control system when the fuel vapor control system is closed. For example, the internal pressure of the fuel vapor control system may be represented by a gas pressure in the fuel tank, and takes an unexpected change if the system has a leak. The leak check can be carried out either when the engine is activated or when the engine is not activated. However, the leak check should be carried out during a time when the fuel vapor control system is in a stable condition. The stable condition may be obtained more frequently when the engine is not activated.
U.S. Pat. No. 5,263,462 discloses the leak check apparatus and method in which the leak check procedure is carried out while the engine is not activated.
Generally, the engine drives a generator to supply electricity to the fuel vapor control system and a battery. Therefore, if the leak check is carried out while the engine is not activated, the battery alone supplies power to the fuel vapor control system. As a result, the battery may over discharge electricity while executing the leak check.
Further, in order to improve an accuracy of the leak check, a period of time for the leak check procedure should be extended as long as possible. However, since a capacity of the battery is limited, it is difficult to obtain such a longer period of time for the leak check.
Further, in order to maintain the fuel vapor control system in a closed condition during the leak check procedure, the valves disposed in the fuel vapor control system also consumes the electricity of the battery.
It is an object of the present invention to provide a fuel vapor control system that is capable of reducing the consumption of electricity for carrying out the leak check.
It is an object of the present invention to provide a fuel vapor control system that is capable of extending a period of time for the leak check that is carried out while the engine is not activated.
According to a first aspect of the present invention, a leak check is carried out after the engine is stopped. During the leak check, the fuel vapor passage is closed as a closed chamber. In the fuel vapor passage, the internal pressure will be changed as the temperature of the fuel vapor is changed after the engine is stopped. The internal pressure of the fuel vapor passage demonstrates an existence of the leak or not. The internal pressure is sampled intermittently. Specifically, the intermittent sampling is carried out by activating a component for sampling the internal pressure. Therefore, the component can be deactivated between the sampling timings. It is possible to reduce the consumption of electricity.
According to the present invention, it is possible to monitor the internal pressure for a long period of time with small power consumption. Therefore it is possible to keep electricity of the battery (i.e. maintain battery life).
According to another aspect of the present invention, the fuel vapor passage is closed by at least one valve that is capable of maintaining a closed condition without activation. Therefore, it is possible to reduce the consumption of electricity for activating the valve during the leak check.